Algorithm for radar coordinate conversion in digital scan converters

Abstract

Disclosed is a system for high speed conversion of radar formats from polar coordinates to cartesian coordinates. From an initial address X i Y i where a radar pulse crosses a display, subsequent addresses are determined by adding constant values sin θ i and cos θ i to X i and Y i . This is faster than the prior method of calculating x i and Y i by multiplying R i (range) by sin θ i and cos θ i . Also disclosed is a system for filling the display between adjacent radials at long ranges where spoking of the display tends to occur. This is done by adding constant increments to one cartesian value on one vector until the next vector is reached while maintaining the other cartesian value constant.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 
     
       1. A system for high speed coversion of polar coordinates of radar returns from radially spaced apart radar pulses into cartesian coordinates for storage in a digital memory comprising means for determining an initial X i ,Y i  address corresponding to where a radar pulse crosses a raster display at an angle θ i , means for determining subsequent addresses X i+1  and Y i+1  for said pulse by adding constant values sin θ i  and cosθ i  to X i  and Y i , means for storing data representative of said radar returns at said addresses X i  and Y i , and means for filling said display between adjacent radar pulses at ranges where spoking tends to occur with data related to the data stored at each address X i , Y i . 
     
     
       2. A system as claimed in claim 1 wherein said means for filling comprises means for sequentially adding constant increments to one cartesian value of one vector until a next vector is reached while maintaining another cartesian value constant. 
     
     
       3. A system as claimed in claim 1, wherein said means for filling comprises means for sequentially addressing a plurality of locations spaced apart along one cartesian axis from a location representing one radar pulse to a location representing a subsequent radar pulse while maintaining a constant value for the address along the other cartesian axis. 
     
     
       4. A system as claimed in claim 3, wherein said locations are spaced apart a constant distance for any two adjacent radar pulses. 
     
     
       5. A system for high speed conversion of polar coordinates of radar returns from radially spaced apart radar pulses into cartesian coordinates for storage in a digital memory comprising means for determining an initial X i , Y i  address corresponding to where a radar pulse crosses a raster display at an angle θ i , means for determining subsequent addresses X i+1  and Y i+1  for said pulse by adding constant values sin θ i  and cosθ i  to X i  and Y i , means for storing data representative of said radar returns at said addresses X i  and Y i , and means for filling said display between adjacent radar pulses at ranges where spoking tends to occur with data related to the data stored at each address X i , Y i , said means for filling comprising means for sequentially addressing a plurality of locations spaced apart along one cartesian axis from a location representing one radar pulse to a location representing a subsequent radar pulse while maintaining a constant value for the address along the other cartesian axis, said locations being spaced apart a constant distance for any two adjacent radar pulses, and wherein said distance is cosθ tanθ' for filling along the x-axis and r sinθ cotθ' for filling along the y-axis, wherein θ is the angle between said first radar pulse and the y-axis and θ' is the angle between said subsequent radar pulse and the y-axis. 
     
     
       6. A system as claimed in claim 5, including means to stop said means for filling at or before an address representing said subsequent radar pulse.